Stem rust (Puccinia graminis fsp. tritici) has dark brown pustules that can tear through either leaf surface and spread to stems and spikes. It appears late in the season particularly in humid, warm areas (15-30°C).

Leaf rust (Puccinia recondita) produces light brown spores mostly on the upper surface of the leaf. It causes no rupture of the epidermis. As with stem rust, the pustules may spread to stems late in the season. Leaf rust is in all cereal growing areas. It thrives in moist conditions with temperatures of 15-25°C.

Look for blotches with yellow margins on your crop leaves. Blotch diseases are more difficult to identify than rusts, but check the descriptions below.

Septoria tritici (blotch) produces irregular lesions with black specks. Septoria nodorum (glume blotch) produces lesions that have no black spot. Late in the season and under humid, warm conditions, the disease infects the glumes and spike causing grey blotching and shrivelled seeds.

Tan spot (Pyrenophera repentis) produces symptoms that are similar to those of glume blotch, but the disease occurs in cool climates and is restricted to leaves.

Spot blotch or leaf blight (Bipolaris sorokiniana) has become significant in the warmer humid areas of SE Asia causing major yield losses in Bangladesh (Alam et al 1994). It can be seen as small blotches with minimal necrosis on the lower leaves of seedlings, but during stem elongation and heading it can spread rapidly up the plant to damage most leaves and eventually infect the seed with black point.

Solutions to disease

Rusts & powdery mildews

Variety: Sow more resistant varieties, and change varieties as often as practicable.

Rotation: Avoid monoculture of a variety over large areas.Fungicides: Apply fungicides if an epidemic level is reached, particularly for yellow rust.

Fertilizer: Avoid excess application of nitrogen fertilizer.

Smuts

Variety: Use resistant varieties.

Clean seed: Use only clean seed harvested from a clean field. Ensure the harvester is not contaminated from the previous field

Seed treatment: Use treated seed or treat at the farm using available recommended fungicide.

Shallow planting: Avoid deep planting particularly in fields where smut disease was present in previous years.